1. Field of the Invention
The present invention relates to tooling machinery and more particularly to alignment plates for holding and aligning a workpiece.
Machinery which is used to perform a variety of tooling operations on a workpiece, such as drilling and routing, is often automated. For example, a machine can be programmed with a set of instructions to perform a series of drilling operations at predetermined locations on a workpiece such as a stack of printed circuit boards. The machine typically has a movable worktable which sequentially moves the workpiece beneath a tooling element such as a drill so that the proper locations on the workpiece are drilled. It is important for the workpiece to be properly aligned on the worktable so that the machine "knows" where the workpiece is. In other words, the workpiece must be accurately positioned relative to an origin or "starting point" on the worktable and then secured to prevent the workpiece from shifting on the table. With the workpiece so aligned, the machine may be programmed to perform various tasks at particular locations on the workpiece measured with respect to the starting point. To this end, workpieces are often provided with a plurality of alignment pins which fit into alignment holes and slots in an alignment plate which is in turn fastened to the worktable.
2. Description of the Prior Art
Prior alignment plates have typically comprised a rather large and thick metal plate which is bolted to the worktable, as shown in FIG. 1. The plate often has an alignment hole bored into the plate and a cavity excavated from the top side of the plate. Two alignment bars are glued into the cavity with epoxy glue and spaced from each other to form an alignment slot between the bars. The alignment pins of a workpiece, such as a stack of printed circuit boards, are then inserted into the alignment hole and alignment slot which aligns the workpiece relative to the worktable. At the end of the tooling operation, the completed workpiece is removed from the alignment plate and a new workpiece to be tooled is inserted into the alignment plate.
One disadvantage of these prior alignment plates is that they typically can accomodate only one size alignment pin, since the diameter of the alignment hole and width of the alignment slot are fixed. These alignment plates are also relatively difficult to fabricate, since the alignment bars must be carefully glued into position relative to the alignment hole and the bolt holes through which the plate is fastened to the worktable. Also, the alignment plates often are very thick to allow the cavity to have a sufficient depth and hence tend to be very heavy. Since the worktable to which the alignment plate is fastened often moves to position the workpiece under the tooling element, the use of a heavy alignment plate can result in slower movement, which reduces efficiency and makes the operation less economical. Furthermore, machinery components located below the surface of the worktable often need to be accessed, which generally requires the removal of the alignment plate. Hence, the positions of the alignment hole and alignment slot with respect to the table are disturbed and the alignment plate must be carefully realigned when it is replaced onto the work table.
Accordingly, a practical alignment device should be lightweight and capable of accomodating a variety of alignment pin diameters. Furthermore, the alignment device should provide access to the worktable without necessitating disturbing the alignment hole and alignment slot positions.